Yes but there's a difference between a VC investing a billion dollars in one startup and one investing $100K each in a thousand of them. In the first case they will obviously do a ton of due diligence, go over business plans, get board seats, look at code and more. YC on the other hand has a 10-minute chat with the founder and...that's it.
The earlier you invest, the larger the risk and looser the diligence.
The earlier you invest, the larger the risk and looser the diligence.